FYI, I have a 8'x4'x30" tank with 2 TSNs and 1 RTCxTSNs (as well as a couple others) who are less than 1 1/2 years old ranging from 24-26". I'm crossing my fingers this will hold them for another 1-1.5 years, but I'm not sure this will. I'm going to say for life you look at a very bare minimum of 12'x6'x3.5" to keep them wet and at least be able to turn around, but this will still be a tight fit and they won't be able to swim that well. Round stock ponds like a 12' round is better for them so they don't trash around as they try to turn.
I must of got a midget tsn.